Non-polarized d. c. transistorized telemetering amplifier



Dec. 15, 1964 E. J. ROSS 3,161,333

NON-POLARIZED D.C. TRANSISTORIZED TELEMETERING AMPLIFIER Filed Aug. 18, 1961 INVENTOR Edward Jasep/r Ross BY fi y ATTORNEY United States Patent 3,161,833 NON-POLARIZED D.C. TRANSISTORIZED TELEMETERING AMPLIFIER Edward .loseph Ross, McKeesport, Pa., assignor to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 18, 1961, Ser. No. 132,396 Claims. (Cl. 330-24) My invention relates to a transistorized nonpolarized D.C. telemetering amplifier. One of the objects of my invention is to provide a construction of DC. amplifier which will function efliciently regardless of the polarity of the DC. voltage applied to its input.

Another object of the invention is to provide a construction of non-polarized D.C. telemetering amplifier which is operable on low D.C. voltages.

A further object of my invention is to provide a construction of transistorized D.C. telemetering amplifier which is applicable for use on existing D.C. transmission liries in underground mines and the like, where line losses are usually at a maximum and transmitting battery voltages are required by law to be maintained at low values.

Other and further objects of the invention reside in the circuit construction and the manner in which the DO. amplifier may be made to respond to low frequencies up to the audio range by adjustment of certain circuit parameters as set forth more fully in the specification hereinafter following by reference to the accompanying drawing which shows the electrical schematic diagram of the non-polarized D.C. transistorized telemetering amplifier of the invention;

In underground mining it is often desirable to remotely indicate or control a given function such as a relay or audio amplifier by way of an existing transmission line such as a twisted pair of telephone lines which are most often used in such cases. The twisted pair of telephone lines, making up the transmission line in such an application, is often saturated with moisture and rock dust so The collectors 17 and 18 of transistors 7 and 8, respectively, are connected to one side of the load 19 by means of conductors 20 and 21, while the other side of the load is connected to the negative terminal of battery 11. Thus the load 19 is in series with battery 11 and is connected in common with both of the transistors 7 and 8 through their collector circuits. The load 19 can be a relay, an indicator to denote a potential on the transmission lines, or any other type of load that is required to perform a desired function. A bypass capacitor 22 is connected across load 19 to bypass any A.C. current that the line losses are great and the line thus presents substantial attenuation to a transmission signal. Excessive battery voltages are not permitted for use in mines by law and, therefore, the maximum distance that a D.C. signal of the magnitude permitted by law can be transmitted under these conditions is very limited. The use of the existing transmission lines in mines is most frequently desired for economical reasons and, thus, to elficiently use such transmission lines, there is need for a DC. telemetering amplifier which will operate efi'iciently where excessive line losses and/or low battery transmission voltage requirements exist. The non-polarized D.C. telemetering amplifier circuit of the present invention was designed to operate under such adverse conditions and may be utilized to remotely energize a relay or the like for performing a desired function. It is to be understood, however, that the amplifier can also be utilized to perform in environments other than mines.

In the accompanying drawing, reference characters 1 and 2 designate the lines of a DC. transmission line, wherein a pair of choke coils 3 and 4 are respectively connected to transmission lines 1 and 2, and their opposite ends are respectively connected to the bases 5 and 6 of the PNP type transistors 7 and 8. The emitters 9 and 10 of transistors 7 and 8 are respectively connected through potentiometers 12 and 13 to the positive terminal of battery 11 which provides the operating potential for the circuit. The movable elements 14 and 15 of potentiometers 12 and 13 are ganged on a common shaft as indicated at 16 so that they will move in unison and function as a sensitivity control adjustment for the non-polarized D.C. amplifier of the invention.

which may be present at the collectors 17 and 18 of transistors 7 and 8. Capacitor 22 also functions to provide a time delay in those applications where the load 19 is a relay coil.

A diode 23 is connected between the base 5 of transistor 7 and the positive terminal of battery 11 in such a manner that diode 23 will conduct when a volt-age of positive polarity appears on transmission line 1. Thus the diode acts as a switch connected across the base-emitter circuit of transistor 7. A capacitor 24 of large value is connected in parallel with diode 23 and assists in bypassing any A.C. voltages appearing across the diode.

A diode 25 is connected between the base 6 of transistor 8 and the positive terminal of battery 11 in such a manner as to conduct only when a positive voltage polarity is present on transmission line 2. Therefore, this diode performs as a switch across the base-emitter circuit of transistor 8. Similarly, as in the circuit of transistor 7, a capacitor 26 of large value is connected across diode 25 to assist in bypassing any A.C. voltages appearing across this diode.

Thus, choke coil 3, diode 23, diode 25 and choke coil 4 are connected across transmission lines 1 and 2, and any voltage appearing on the transmission lines will be impressed across these circuit elements. For purposes of illustrating the operation of the non-polarized D.C. telemetering amplifier circuit of the invention, assume a voltage of negative polarity appears on transmission line 1 and a voltage of positive polarity appears on transmission line 2. Choke coils 3 and 4 will appear as a low resistance path to the DC. voltage appearing on the transmission lines, but will appear as a high reactance to any A.C. signals which might appear on these lines. Therefore, the DC. signals on lines 1 and 2 will appear across the identical diodes 23 and 25. As previously stated, each of the diodes is connected so that it will conduct only when a voltage of positive polarity appears on the transmission line with which it is connected. Thus, since a voltage of positive polarity appears on line 2, diode 25 will conduct, presenting a low resistance path or a virtual short circuit across transistor 8. On the other hand, since a voltage of negative polarity appears on line 1 diode 23 will not conduct and will thus represent a large resistance across transistor 7. Thus, depending on the polarity of DC. on the lines 1 and 2, diode 23 or diode 25 will conduct to electrically connect either transistor 7 or 8 across lines 1 and 2. Therefore, in the present illustration, diode 25 conducts to short circuit transistor 8 and electrically connect the emitter 9 of transistor 7 to line 2 through choke coil 4. Since transistors 7 and 8 are PNP type transistors, they require a negative voltage on the base with respect to the emitter to cause conduction of the transistors. Therefore, transistor 7 will conduct since a voltage of negative polarity appears on line 1 and the base 5 of transistor 7 is connected to the line 1 through choke coil 3. At the same time, transistor 8 will be cut oif.

As stated, the operating potential for the circuit is provided by battery 11 which is connected in common with the emitter circuits of both transistors 7 and 8.

With transistor 7 conducting, D.C. current will flow through the load 19 at an amplified rate, causing a voltage drop across the load and thus energizing the same if the load is a relay coil or an indicator.

When the polarity is reversed on lines 1 and 2, that is, when a voltage of positive polarity appears on line 1 and a voltage of negative polarity appears on line 2, diode 23 will conduct short circuiting transistor 7, causing the same to be in a state of cut-off, while diode 25 does not conduct, causing transistor 8 to be connected across lines 1 and 2 in a state of conduction. This then causes a D.C. current to again flow through load 19 at the amplified rate and in the same direction. The switching action and the rate at which transistors 7 and 8 are turned on is dependent upon the voltage-current characteristics of the diodes used and it has been found that the circuit operates best with diodes having a low forward resistance and a high front-to-back resistance ratio. It has been found that the selection of the transistors is not critical except that a low collector current (I is required. The circuit of my invention has application where multiple transmission lines are used, wherein the received signal can also be utilized to retransmit over another pair of transmission lines, by means of a relay and battery, to indicate that the transmission was received and/ or the desired function was performed by means of the load circuit of the present D. C. amplifier. By reversing the operation in this manner a closed loop system is formed wherein the transmission line network is disposed to check its own system and the continuity of the transmission lines utilized.

The value of the capacitors 24 and 26, along with the values of the chokes 3 and 4, determines whether or not the amplifier will pass any range of frequencies. It has been found that the D.C. amplifier of the invention can be made to respond to low frequencies up to approximately fifty cycles, as well as D.C. voltages by varying the values of capacitors 24 and 26, and choke coils 3 and 4. For example, if a low frequency A.C. signal is impressed on the transmission line, along with a D.C. voltage, the D.C. amplifier acts as a D.C. gate to this audio signal. The D.C. amplifier recognizes the presence of the D.C. signal and this D.C. voltage will operate the D.C. amplifier to open the gate to allow the audio signal to pass. This is accomplished by means of a load relay in the D.C. amplifier circuit disposed to energize an audio amplifier when the D.C. signal is present on the transmission lines. The audio amplifier can thus function to further amplify the AC. signal appearing on the line with the D.C. signal. When the low frequency A.C. signal alone is present on the transmission line the D.C. amplifier of the present invention will not operate to pass the signal.

It can, therefore, be seen that the D.C. telemetering amplifier of the present disclosure is non-polarized and can be connected to any D.C. transmission line without first determining the polarity of the line, since the amplifier will operate no matter what the polarity of the transmiscion line due to its non-polarized circuit construction. While I have described my invention in one of its preferred embodiments, I realize that modifications may be made, and I desire that it be understood that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is as follows:

1. A non-polarized D.C. amplifier comprising a pair of semiconductor devices of the same conductivity type, each including base, emitter and collector circuits, load circuit means including a source of potential for operating said semiconductor device, said collector circuits coupled in common to one side of said load circuit means, said emitter circuits coupled in common to the other side of said load circuit means, A.C. choke means connected individual to the base circuit of each of said semiconductor devices, input circuit means connected to the other ends of said A.C. choke means, unidirectional conducting means connected between the base and emitter circuits of each of said semiconductor devices with the direction of conduction of each opposite to that of the associated semiconductor device, and one of said unidirectional conducting means and the opposite semiconductor device disposed to conduct to energize said load circuit means upon presence of a D.C. voltage of one polarity on said input circuit means and the other of said unidirectional conducting means and its opposite semiconductor device disposed to conduct to energize said load circuit means upon presence of a D.C. voltage of opposite polarity on said input circuit means.

2. A non-polarized D.C. amplifier, as set forth in claim 1, in which said emitter circuits each includes resistance means commonly connecting the same.

3. A non-polarized D.C. amplifier, as set forth in claim 1, including A.C. bypass means connected between the base and emitter circuits of each of said semiconductor devices.

4. A non-polarized D.C. amplifier as set forth in claim 1 in which said semiconductor devices are each of the type which conduct when a potential of negative polarity with respect to the emitter is applied to the base circuit.

5. A non-polarized D.C. amplifier comprising first and second semiconductor means each having base, emitter and collector circuits, a pair of input circuits, first choke means connected between one of said input circuits and the base circuit of said first semiconductor means and second choke means connected between the other of said input circuits and the base of said second semiconductor means, first and second unidirectionally conductive means connected to conduct in a direction opposite to that of the associated semiconductor means connected between the base and emitter circuits of said first and second semiconductor means, respectively, a source of biasing potential, said emitter circuits of said first and second semiconductor means connected in common to said source of potential, load means connected with said source of potential, and said collector circuits of said first and second semiconductor means commonly connected to the opposite end of said load means for energizing said load means by conduction of either said first or second semiconductor means determinative on the D.C. voltage polarity on said pair of input circuits.

References Cited in the file of this patent UNITED STATES PATENTS 2,864,904 Jensen Dec. 16, 1958 2,926,267 Radcliffe et al. Feb. 23, 1960 3,015,780 Schayes et al. Jan. 2, 1962 

1. A NON-POLARIZED D.C. AMPLIFIER COMPRISING A PAIR OF SEMICONDUCTOR DEVICES OF THE SAME CONDUCTIVIT Y TYPE, EACH INCLUDING BASE, EMITTER AND COLLECTOR CIRCUITS, LOAD CIRCUIT MEANS INCLUDING A SOURCE OF POTENTIAL FOR OPERATING SAID SEMICONDUCTOR DEVICE, SAID COLLECTOR CIRCUITS COUPLED IN COMMON TO ONE SIDE OF SAID LOAD CIRCUIT MEANS, SAID EMITTER CIRCUITS COUPLED IN COMMON TO THE OTHER SIDE OF SAID LOAD CIRCUIT MEANS, A.C. CHOKE MEANS CONNECTED INDIVIDUAL TO THE BASE CIRCUIT OF EACH OF SAID SEMICONDUCTOR DEVICES, INPUT CIRCUIT MEANS CONNECTED TO THE OTHER ENDS OF SAID A.C. CHOKE MEANS, UNIDIRECTIONAL CONDUCTING MEANS CONNECTED BETWEEN THE BASE AND EMITTER CIRCUITS OF EACH OF SAID SEMICONDUCTOR DEVICES WITH THE DIRECTION OF CONDUCTION OF EACH OPPOSITE TO THAT OF THE ASSOCIATED SEMICONDUCTOR DEVICE, AND ONE OF SAID UNIDIRECTIONAL CONDUCTING MEANS AND THE OPPOSITE SEMICONDUTOR DEVICE DISPOSED TO CONDUCT TO ENERGIZE SAID LOAD CIRCUIT MEANS UPON PRESENCE OF A D.C. VOLTAGE OF ONE POLARITY ON SAID INPUT CIRCUIT MEANS. 